Method of forming mold patterns



equally spaced and parallel sections Patented Sept. 16, 1941 PATENTOFFICE 2,256,338 METHOD. OF FORMING MOLD PATTERNS Joseph B. Brennan,Cleveland, Ohio No Drawing. Application Serial No.

1 Claim.

This invention relates to the art of casting metals, and moreparticularly to an improved method of making patterns, templets and thelike, to be used in making molds for castings.

As is well known, patterns are employed to 5 shape the mold into whichmolten metal is cast, in making the casting. Since the metal will shrinkupon cooling, it is necessary that the pattern and mold be madesufliciently larger than the finished casting to compensate for suchshrinkage.

The usual practice in the production of a casting, begins with thepreparation of a drawing which is made to the scale of the finishedcasting. From this drawing, the pattern-maker will build a facsimile orpattern which is used to shape the mold for the casting. Thepatternmaker, in building the pattern, must allow for the shrinkage ofthe cast metal which will vary between one-eighth and one-quarter inchper foot, according to the kind of metal which is being used in makingthe casting. The patternmaker, in laying out the pattern, is not able totake the dimensions of the pattern directly from the drawing of thecasting, but must resort to a shrink rule or calculate the amount ofshrinkage that will take place in order to build the pattern to thedesired size. Diflicult and time-consuming operations which require theservice of skilled workers are thus encountered.

In the case of large castings or castings of an extremely irregularcontourwhich cannot readily be made from a single piece of material, thepattern is usually made of sections of wood or metal, and the finishedpattern is completed by piecing such sections together. Another commonway of building patterns for such castings, is to make a series ofdrawings corresponding to of the casting, and form templetscorresponding to such sections. These templets are then used to form askeleton-like reproduction of the casting which may be filled in to formthe finished pattern in a manner well known in the art. The accuratebuilding of a pattern from sections pieced together is rendereddifficult due to the fact that an error in the size of one of thesections will usually result in such error being transmitted to anadjacent section.

Castings which require the accurate reproducion of an irregular contour,such as a surface having a small radius of curvature, are almostimpossible to reproduce in the form of a pattern which will accuratelytake into account the shrinkage that will take place in such surface. 55

December 16, 1940, 870,375

For example, where the dimensions of the material forming such surfaceare in odd fractions of an inch, an extremely small and unmeasurablefraction of an inch must be added to compensate for the shrinkage whichwill take place. In such cases, the pattern-makers usually make suchsurfaces considerably over-size in order to be certain that the castingwill not be undersize with respect to such surfaces.

time-consuming grinding and machining operations.

. One of the principal objects of this invention is to provide animproved method of laying out a pattern to pattern size on the materialfrom which the pattern is to be made, which will eliminate the humanerrors normally encountered in laying out such pattern by the use of ashrink rule, or by the employment of mental calculations.

A further object is to provide an improved method of forming a moldpattern in which the shape of the pattern is photographically reproducedto pattern size on the material from which the pattern is to be made.

A further object is to provide an improved method of forming a moldpattern in which a drawing to finished-scale is photographicallyreproduced to pattern size on the material from which the pattern ismade.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described, andparticularly pointed out in the claim, the following description settingforth in detail certain illus trative embodiments of the invention,these being indicative however, of but a few of the various ways inwhich the principle of the invention may be employed.

The method of this invention is particularly adapted for use inconnection with patterns which are made up from sections in the natureof templets, and in which the templets are formed by laying out thedesired contour of the section on the plate, and then cutting away thematerial lying without the confines of the contour as laid out.

In carrying out the method of this invention, a drawing of the castingis made to finished scale size in accordance with a conventionalpractice. The drawing is then photographically reproduced to patternsize on the surface of the material from which the pattern is to bemade. In reproducing the drawing to pattern size on the surface of thematerial from which the pattern is to be made, the surface of suchmaterial is first sensitized to receive a photographic reproduction bythe application to such surface of a light-sensitive substance, whichsubstance may be of any kind now commonly employed in the photographicart. Since many types of apparatus are available for reproducing adrawing on such a sensitized surface, it is not believed necessary tospecifically refer to the construction or operation of such apparatus,any suitable apparatus capable of enlarging the drawing accurately, asufficient percentage to compensate for a predetermined shrinkage beingemployable for the purposes of carrying out themethod of this invention.

In the preferred practice of this invention, it is desirable that thedrawing to be reproduced be made to full scale of the finished casting,and an enlarged reproduction of such drawing is then photographicallytransmitted to the surface of the material from which the pattern is tobe made, the enlargement being sufficient to compensate for theshrinkage which will take place upon cooling of the casting metal.However, it will be understood that the invention is. applicable to anycase, wherein the original drawing is made to a scale other than a fullscale size, the photographic reproduction apparatus being availed of insuch case to compensate, for example, those cases wherein the originaldrawing is made to one-half or one-quarter size.

To reproduce the casting or finished product to pattern size on thematerial from which the pattern is to be made, it will be firstnecessary to make a negative of the original drawing. The negative whichis thus made may be either of the same size as the original drawing ormay be enlarged to pattern size or an amount sufficient to compensatefor the shrinkage which will take place upon cooling of the moltencasting metal. Whether or not the negative is or is not enlarged will bedependent upon the particular step in the reproducing of the drawing topattern size on the material from which the pattern is being made inwhich the enlarging of the original drawing takes place. If the negativeis made to the same size as the original drawing, it will be necessaryto employ the photographic enlarging apparatus in reproducing thedrawing on the sensitized surface. If the photographic enlargingapparatus is employed in making the negative of the drawing, then itwill only be necessary to reproduce such negative on the sensitizedsurface by the conventional photographic methods of preparing a positiveprint from a negative print. If desired, the enlarged negative may beformed directly upon the sensitized surface, and in such case, if themold pattern section is in the form of a flat templet, the step ofactually reproducing a negative print prior to transmittal to thesensitized surface will be eliminated. The preferred practice, for mostcases, will be'to employ the photographic enlarging step in thepreparation of the negative.

Regardless of the step in which the photographic enlarging operationtakes place, the apparatus by which such enlargement is made will befound to employ a. lens which must be adjusted relatively to the surfaceof the drawing and to the surface on which the negative is to be formedin order that the object and image focal distances will be proper tosecure the desired enlargement. It is contemplated that the parts bywhich such adjustments are made be promade.

vided with suitable scales and indicia setting corresponding to thematerial to be worked with. There would be thus different settings forthe different metals to be worked with, and it would be merely necessaryfor the operator to move such parts to the setting for cast iron tosecure the desired adjustment if cast iron is the material from whichthe casting is to be made; and likewise, there would be provided similaradjustments for copper, steel, bronze, and other metals.

In this way, it is possible to produce the mold pattern to exact patternsize without the employment of a shrink rule or mental calculations. Ifthe metal worked with has a shrinkage of /4 inch per foot, thephotographic enlargement can be made to add V to the size of every partregardless how small, such reproduction being virtually impossible wherea shrink rule is employed.

Although the preferred practice has been described for the case whereinthe drawing is reproduced directly upon the surface of the material fromwhich the section is to be made, it will be understood that thisinvention is intended to have a field of use wherein the nature of thecasting is such as to prevent such direct reproduction. In such case,the original drawing need not be directly reproduced to pattern size onthe material by photographic methods, and there need be formed only aphotographic enlargement or print of the drawing. The pattern maker willthen make the pattern in the usual manner and obtain his measurementsdirectly from the enlarged print through the use of dividers orcalipers.

In those cases where it is desired to construct an unusually strongpattern from steel templets formed in accordance with the principles ofthis invention and arranged at spaced intervals to form the skeleton ofthe pattern, the templets may be bolted or welded together to form arigid framework. Such framework may then be filled in to complete thepattern with plaster or other suitable molding materials, such ascertain well known pheno-formaldehyde compounds which set at roomtemperatures. -In connection with the material from which the templetsare made,

it will be understood that plywood or any other material capable oftaking a sensitized photographic plate may be employed.

Where metallic templets are employed, it will be apparent that theprocess of this invention permits the use of etching as a means ofsecuring a clean delineation of the contour of the drawing transferredto such plate. If the metal from which the templet is formed issufiiciently thin, the etching may be employed to remove the excessmaterial surrounding the templet in place of other cutting operations.

The process of this invention provides important advantages in theconstruction of large castings, such as dies. In such case, patterns canbe made to /8 or A size from which a miniature model of the die, orother casting, may be The model may then be tried out to see how themetal will flow in a press, if the model be a die, and to observe othercharacteristics which it is often important to know before constructinga full size die which may weigh many tons. Any correction needed maythen be made in the pattern or model of reduced size. Thereafter themodel or pattern can be cut up into sections and photographs of suchsections can be employed in the construction of the full size model. Insuch case, the photographs would be enlarged to full size plus anyallowance desired for shrinkage.

In those instances, wherein reference is made to a drawing in thisapplication, it will be understood that the dimensions of such drawingdo not take into consideration the shrinkage which will take place uponcooling of the cast metal. It will also be understood that where theterm photographically reproducing such drawing to pattern size" isemployed, there is meant a reproduction which has been mechanicallychanged by the photographic reproducing apparatus to compen sate for themetal shrinkage.

From the foregoing, it will be apparent that the method of thisinvention enables the production of a pattern which will accuratelycompensate tor the shrinkage of the cast metal regardiess of anyirregularities or odd shape in the suriace oi the finished casting. Bythis method, the expensive grinding and finishing operations heretoforeemployed and necessary to finish the casting to size are therebysubstantially eliminated.

Other modes oi applying the principle oi-the invention may be employed,change being made as regards the details described, provided thefeatures stated in the following claim, or the equivalent of such, beemployed.

I therefore particularly point out and distinctly claim as my invention:

In the method or forming a mold pattern, the

steps which comprise preparing a drawing in accordance with the exactdimensions of the 11mished casting, phctographically reproducing andenlarging said drawing an amount suiiicient to compensate for theshrinkage of the metal to be employed in making the casting, andemploylng said photographic enlargement to secure the dimensions of thepattern.

JOSEPH B. BRENNAN.

